Respiration of air-

The major impurities in the expired air are carbon di-oxide, water vapours and organic matter . when the amount of air of a particular room rises to above person, the air becomes stuffy, however stagnation of air and reduced oxygen are the contributory factors to cause symtoms like drowsiness, headache, nausea etc. in over-crowded rooms. In case of persons suffering from pneumonia, diphtheria, tuberculosis etc. microbes in large numbers may come out during coughing, sneezing loud-speaking.